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W polarization study in ttbar semi-lep decay

W polarization study in ttbar semi-lep decay. BoLi Shandong University. W polarization in top decay. Test the top decay (in fully reconstructed tt) with W polarization. ...by measuring angular distribution of charged lepton in W rest frame. n. Angle between:

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W polarization study in ttbar semi-lep decay

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  1. W polarization study in ttbar semi-lep decay BoLi Shandong University

  2. W polarization in top decay • Test the top decay (in fully reconstructed tt) with W polarization ... • ...by measuring angular distribution of charged lepton in W rest frame n • Angle between: • lepton in W rest frame and • W in top rest frame b W+ t  1/2 spin

  3. Data New data sample (re-reconstructed MC08 with rel. 15.3.1.6) and rel.15.6.0 for analysis MC@NLO tt samples: mc08.105200.T1_McAtNlo_Jimmy.merge.AOD.e357_s462_s520_r809_r838 AcerMC tt samples: mc08.105205.AcerMCttbar.recon.AOD.e429_s462_s520_r808 mc08.105205.AcerMCttbar.merge.AOD.e429_s462_s520_r808_r838 MC08 background samples(s520_r808_r838): w+jets (Alpgen 106280-3,107682-5,107692-5,107702-5) z+jets (Alpgen 107652-5, 107662-5,107672-5) dibosons(Herwig 105985-7) single top(AcerMC 105500,105502)

  4. event selection 68%(64%) =1 lepton isolated |eta|<2.5 pT>20GeV for μ pT>25GeV for e 57%(57%)≥ 4 jetspt>30GeV |eta|<2.5 33%(33%)≥2 bjets btagged with jetprob<0.014@eff~60% • 90%(90%)etmiss>20GeV • Final kinematic cut efficiency 11.5(11.1)%

  5. Event reconstruction whad = 2 jets (mass closest to 80.4GeV) thad = whad + bjet (mass closest to 175GeV) Possible wlep= l +ν (constraint of Mw=80.4GeV) tlep = bjet + wlep (bjet dR closest to lepton) (mass closest to 175GeV) reconstruction efficiency 3.39%(3.14%) Plus quality cut ( |Mwhad-80.4 |<20 and |Mt – 175|<35 )

  6. Data

  7. Measurement method Correction function : • Selection cuts and reconstruction distort the parton lever distribution • Use an independent sample to correct this distortion. parton level Reconstruction and cuts

  8. Measurement method The tau events not correctly reconstructed as the neutrino from tau decay contaminate the neutrino from w decay Taking e/mu/tau as signal instead of e/mu at parton level distribution

  9. Truth values get from parton level distribution

  10. Result Function fit for w polarization Measured value with statistical error: FL= 0.281± 0.023 F0= 0.754± 0.042 FR=-0.034± 0.023

  11. Result Systematic error

  12. Result Correction function use MC@NLO tt sample

  13. Summary • Use new samples and software at r15 The selection efficiency increase from11.1% to 11.5% reconstruction efficiency increase from 3.14% to 3.39% s/b from 8.6 to 9.0 • Taking e/mu/tau as signal result matched well with theoretical value

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